As an important achievement during development of semiconductor industry, memories play an irreplaceable role in our today's society which takes information technology as a foundation. In mobile phones, personal computers, music players, and various handheld devices and vehicle-mounted devices, memories are used in almost every aspect. With development of the semiconductor industry, there are more and more demands on capacity of the memories. From a conventional magnetic resistance hard disk driver to a flash memory, current products are difficult to satisfy the demands on the capacity of memories, thereby to promote an emerge of some new memories, in which a resistive memory (RRAM or ReRAM) is a typical representative.
The resistive memory has a typical structure of MIM (Metal-insulator-Metal), and can achieve a free transition between a high resistance and a low resistance under the control of an external voltage. Howerver, a typical single resistive memory can only perform a two-level storage, greatly limiting a further increased storage capacity of the resistive memory, and thus it becomes a nonnegligible demand that a storage capacity of a single resistive memory is required to be increased, that is, a multilevel storage is required.